1. Field of the Invention
The invention generally relates to the field of magnetic recording. More specifically, the invention relates to thin-film magnetic heads for use in magnetic recording systems wherein the head contacts the media, as in magnetic tape recording. Still more particularly, the invention concerns a tape drive having an improved thinfilm magnetic recording head providing the advantages of superior wear resistance and improved magnetic permeability.
2. Description of the Prior Art
Thin-film magnetic recording heads are manufactured using well-known batch-fabrication techniques in which plurality of head structures are formed on a single wafer substrate by depositing successive layers of material (film layers). Two magnetic film layers are typically used to form a yoke structure. At the forward end of the head, where the head interfaces with the magnetic medium, the magnetic layers are separated by a gap layer of nonmagnetic material to form a pole tip region. Rearwardly of the poles, the magnetic layers are spaced apart to accommodate a flat conductor coil structure which is disposed between the layers. The magnetic layers are then joined rearwardly of the coil structure to form the back gap portion of the head.
In the design of thin-film magnetic recording heads that contact an underlying magnetic medium, such as tape, superior magnetic properties combined with good magnetic characteristics are important concerns. In the past, head designers have utilized layers of PERMALLOY. an 80%/20% NiFe composite, for the poles because of its excellent wear characteristics. Although it has superior magnetic characteristics, permalloy is ductile and will differentially recess when worn with conventional particulate recording media. Pure permalloy poles have been shown to recess too much, eventually preventing the head from writing.
Given the deficiencies of permalloy, head designers have turned in recent years to mechanically hard vacuum deposited films for fabricating the poles because of their excellent wear characteristics. The laminate, however, is difficult to apply thickly, is less magnetically permeable than permalloy, and generally cannot be deposited uniformly across a wafer or from wafer to wafer. These latter problems reduce the writeability of the head and require the drive designer to use expensive adjustable write current technologies.
In order to improve the magnetic properties of laminated film heads, designers have sometimes placed thick permalloy "shaping layers" on top of the upper laminated pole (the P2 pole) in order to decrease the reluctance thereof. The permalloy layer extends from the back gap portion of the head but is recessed from the pole tip because thin poles are considered desirable in order to sharpen the readback response. By recessing the permalloy layer from the air bearing surface (ABS) designers have sought to realize the twin advantages of a thin pole during readback and a low reluctance magnetic path. U.S. Pat. No. 4,878,290 discloses such a design, as do other prior art publications.
Despite prior art efforts to improve the magnetic performance of laminated heads, it has been observed that the data write efficiency of such heads is marginal in many cases. Designers have been plagued with poor yield due to low inductance and high write current requirements, and solutions for solving these problems have not been forthcoming. Accordingly, it would be desirable to provide a thin-film magnetic recording head that satisfactorily optimizes the magnetic properties and wear characteristics of the head in a uniform manner on a single wafer and from wafer to wafer.